1. Field of the Invention
Embodiments of the invention relate to an apparatus and a method for testing a semiconductor device. More particularly, embodiments of the invention relate to an apparatus and a related method adapted to test for leakage current associated with the substrate of a semiconductor device.
This application claims priority from Korean Patent Application No. 10-2005-0065999 filed on Jul. 20, 2005, the subject matter of which is incorporated herein by reference in its entirety.
2. Description of the Related Art
Increased integration density and improved performance are ever present design goals for contemporary semiconductor devices, and the object of ongoing research and development. Increased integration density translates into reduced component size. For example, the insulating layer commonly formed between a transistor and a capacitor is made as thin as possible. However, the performance of this very thin layer must not be degraded. Thus, in order to improve the performance of semiconductor devices incorporating this type of layer, it is important to reliably form the insulating layer with minimal thickness and without defects. In general, a silicon oxide layer (SiO2) has been used to form a gate insulating layer since a conventionally understood fabrication process, whereby a silicon substrate is oxidized to form the desired silicon oxide layer, is simple and very stable. Yet, silicon oxide has a relatively low dielectric constant of about 3.9. Thus, there are very real limits to the minimal thickness of the gate insulating layer formed from silicon oxide. For example, if a gate insulating layer is formed from silicon oxide having a very small thickness, a tunnel current may flow through the gate insulating layer, thereby increasing leakage current for the constituent semiconductor device.
As a result, emerging semiconductor designs use one or more materials to form a gate insulating layer having a dielectric constant higher than silicon oxide. These materials generally allow the formation of a thinner gate insulating layer which serves as an effective replacement for the thicker, formerly used silicon oxide layer. The insulating effect of such “new” layers may be expressed as an “equivalent oxide thickness” relative to the former silicon oxide layer.
The equivalent oxide thickness for a gate insulating layer of given thickness, as formed from a high dielectric material, is typically measured using a corona discharge process. This conventionally understood process begins by depositing charge in a corona discharge state on a selected portion of a semiconductor substrate which is intended to receive the subject gate insulating layer. Then, surface voltage at selected points on the semiconductor substrate are measured with respect to the deposited charge. Lastly, an equivalent oxide thickness is calculated using the slope of a graph relating the amount of the deposited charge with the measured surface voltage of the semiconductor substrate.
However, this conventional testing process suffers from a lack of accuracy. For example, the leakage current generated in relation to the semiconductor substrate being tested is influenced by the deposited charge. That is, there is a difference between the amount of deposited charge and the actual amount of charge remaining on the semiconductor substrate being tested. Thus, it is difficult to accurately calculate the true equivalent oxide thickness. Further, a large difference may exist between the equivalent oxide thickness for the entire semiconductor substrate and the equivalent oxide thickness as measured at the tested portion of the semiconductor substrate. Thus, reliable data on the equivalent oxide thickness for an insulating layer deposited on a semiconductor substrate cannot be provided. As a result, it is difficult to realize a desired equivalent oxide thickness.
At present, there exists no process adapted for use within a mass-production environment that provides high reproducibility and reliability of test measurements for an insulating layer formed from various dielectric materials, including silicon oxide. At a minimum, a more accurate process for measuring an equivalent oxide thickness is needed.